A. Field of the Present Invention
The present invention relates to a device and method for calibrating a linear velocity and a track pitch for an optical disc drive.
B. Description of the Related Art
Optical recording media, such as CD-Rs, CD-RWs, CD-ROMs, DVDs, DVD-RAMs, are usually read by optical disc drives. These optical disc drives correctly control the rotation speed of the spindle motor according to a reproduced sync signal or a motor frequency generator pulse signal. In addition, a precise calculation has to be performed using a “time-to-track” transformation mechanism, so that the laser beam can be shifted to a correct position of the disc (i.e., track jumping). The mechanism of “time-to-track” has to use the parameters of the linear velocity and the track pitch as a calculation basis. According to the current CD standard, the recording linear velocity must be between 1.2 and 1.4 m/s, while the track pitch must be between 1.5 and 1.7 μm. However, the writing speed and track pitch during actual disc playing cannot be predicted. As a result, a slowest writing speed and a maximum track pitch are used as the initial calculation basis in the prior art. Then, the values of the linear velocity and the track pitch are sequentially modified according to the relationship between the track number, which is actually fed back during the track jumping, and the time. However, the laser beam cannot be correctly and quickly shifted to the correct track in this method, thereby wasting a long period of seeking time.
To solve this problem, a method for calibrating an optical disc drive, which controls the spindle motor with a constant linear velocity (hereinafter referred to as CLV), has been disclosed. This method, however, cannot calibrate an optical disc drive, which controls the spindle motor with a constant angular velocity (hereinafter referred to as CAV). The prior art method calculates the linear velocity according to the ratio of the frame-synchronous signal and disk rotation period. In addition, the prior art method can only calibrate the linear velocity with respect to optical discs having data recorded thereon, but not the blank discs.
The linear velocity is an important index for measuring the data amount and is helpful to positioning the laser beam precisely. It is therefore an urgent to-be-solved problem as to how to effectively calibrate the linear velocity and how to apply the calibration method to both the CLV mode and the CAV mode, and to the blank discs.